<!DOCTYPE html>
<html>
<head>
	<title></title>
	<style type="text/css">
		*{
			margin: 0px;
			padding: 0px;
		}
		p{
			margin-left: 4in;
			margin-bottom: 5px;
		}
		div{
			margin-bottom: 5px;
			margin-left: 4in;
			border: 1px solid blue;
			background-color: yellow;
		}
		.a1{
			width: 1em;
		}
		.a2{
			width: 2em;
		}
		.a3{
			font-family:Times New Roman;
			width: 2em;
		}
		.a4{
			width: 1cm;
		}
		.a5{
			width: 1mm;
		}
		.a6{
			width: 1in;
		}
		.a7{
			width: 1ex;
		}
		.a8{
			width: 1pt;
		}
		.a9{
			width: 1pc;
		}
		.a10{
			width: 1px;
		}
		.a10cm{
			width: 10cm;
		}
	</style>
</head>
<body>
	<p>在CSS中，em是非常有用的单位，因为它可以自动适应用户所使用的字体。</p>
	<p>1em</p>
	<div class="a1">我</div>
	<p>2em</p>
	<div class="a2">我们</div>
	<p>英文2em</p>
	<div class="a3">IT</div>
	<br />
	<div class="a4">1cm</div>
	<div class="a5">1mm</div>
	<div class="a6">1in</div>
	<div class="a7">1ex</div>
	<div class="a8">1pt</div>
	<div class="a9">1pc</div>
	<div class="a10">1px</div>
	<div class="a10cm">10cm标准</div>
</body>
</html>